1. Field of the Invention
The present invention relates to a hydraulic circuit for a construction machine, which can implement an auto idle function by automatically reducing revolution of an engine when a working device of the construction machine is not driven.
More particularly, the present invention relates to a hydraulic circuit for a construction machine, which can minimize an energy loss of a hydraulic system by automatically reducing revolution of an engine when a working device such as a boom is not driven.
Hereinafter, in the accompanying drawings, only the construction of pilot signal lines related to an auto idle function is illustrated. When corresponding switching valves are switched, the pilot signal lines are intercepted. The switching state of the valves and the connected lines between a main pump and a working device during the switching operation of the corresponding switching valves are not separately illustrated.
2. Description of the Prior Art
Referring to FIG. 1, a conventional hydraulic circuit for a construction machine having an auto idle function includes first, second, and third hydraulic pumps P1, P2, and P3; a first switching valve A composed of valves installed in a flow path of the first hydraulic pump P1 and shifted to control hydraulic fluid fed to working devices (right traveling motor, arm, boom, bucket, and so forth); a second switching valve B composed of valves installed in a flow path of the second hydraulic pump P2 and shifted to control hydraulic fluid fed to working devices (left traveling motor, arm, option device, and so forth); a third switching valve C composed of valves installed in a flow path of the third hydraulic pump P3 and shifted to control hydraulic fluid fed to a swing device and so on; and a confluence switching valve 8 installed on a downstream side of the flow path of the third hydraulic pump P3 and shifted to selectively supply the hydraulic fluid from the third hydraulic pump P3 to the working devices on the first hydraulic pump side P1 or the working devices on the second hydraulic pump side P2, in response to a pilot signal pressure Pi1 applied thereto.
In a general small-sized excavator, the hydraulic fluid fed from the first hydraulic pump P1 is supplied to the right traveling motor and the hydraulic fluid fed from the second hydraulic pump P2 is supplied to the left traveling motor to drive the traveling motors. In the case of driving other working devices (arm, boom, bucket, and so forth), the confluence switching valve 8 is used to supply the hydraulic fluid fed from the third hydraulic pump P3 to the working devices.
The confluence switching valve 8 is shifted, in response to the pilot signal pressure Pi1 applied thereto, to supply the hydraulic fluid fed from the third hydraulic pump P3 to the working devices (arm, boom, bucket, and so forth) on the first hydraulic pump side P1 or to the working devices (arm, boom, option device, and so forth) on the second hydraulic pump side P2.
The pilot signal pressure Pi1 for shifting the confluence switching valve 8 is supplied from a pilot pump (not illustrated) through a first throttling part 1 installed in a pilot signal line 3.
A signal line 4 includes a signal line 5 passing through the switching valves A and B for the working devices and a signal line 6 passing through a switching valve D for traveling devices. In the case where only either the working devices or the traveling devices are shifted to operate, no signal pressure is formed in the pilot signal line 3.
By contrast, in the case where the working devices and the traveling devices are simultaneously shifted to operate, the pilot signal pressure Pi1 is formed in the pilot signal line 3, and the confluence switching valve 8 is shifted in response to the pilot signal pressure Pi1 formed in the pilot signal line 3. Accordingly, the hydraulic fluid fed from the third hydraulic pump P3 is supplied to the working devices (arm, bucket, boom, and so forth) of the first hydraulic pump side P1 or the working devices (arm, boom, option device, and so forth) of the second hydraulic pump side P2.
In the case of simultaneously implementing the above-described confluence circuit and the auto idle function, it is required to provide a signal device that can sense the shifting of the switching valves for the working devices and the switching valves for the traveling devices. Since the pressure is not formed in the pilot signal line 3 when either the switching valves for the working devices or the switching valves for the traveling devices are shifted, the pressure in the pilot signal line 3 cannot be used as an auto idle signal pressure.
That is, in the case of shifting the switching valves for the working devices or the switching valves for the traveling devices, a separate signal line 7 that can sense the shifting is required. The signal line 7 is connected to the signal line for supplying the pilot signal pressure to the confluence switching valve 8 and is connected to a flow path in which a second throttling part 2 is installed. In addition, the signal line 7 is constructed to pass through all the switching valves A, B, C, and D for the working devices and the traveling devices.
Accordingly, in a neutral state of the switching valves A, B, and C connected to the first to third hydraulic pumps P1, P2, and P3, respectively, it is judged that no signal pressure is formed in the signal line 7 and the working devices do not operate, and the engine revolution of the heavy equipment is automatically reduced. In the case of shifting at least one of the switching valves A, B, C, and D, the signal pressure is formed in the signal line 7, and thus the engine revolution can be accelerated by the formed signal pressure.
Referring to FIG. 2, another conventional hydraulic circuit for a construction machine having an auto idle function includes a confluence switching valve 8 that is shifted by a pilot signal pressure Pi1 fed through a third throttling part 11 formed in a pilot signal line 13; a signal line 15 which is connected to the pilot signal line 13 and in which a signal pressure is formed when switching valves A and B for working devices are shifted; a signal line 16 which is connected to the pilot signal line 13 and in which a signal pressure is formed when a switching valve D for working devices is shifted; and a signal line 17 which is connected to a pilot signal pressure Pi2 formed through a fourth throttling part 12 and in which a signal pressure is formed when the switching valves A, B, C, and D for the working devices and the traveling devices connected to first to third hydraulic pumps P1, P2, and P3, respectively, are shifted.
The conventional hydraulic circuit of FIG. 2 further includes the first, second, and third hydraulic pumps P1, P2, and P3; the first switching valve A composed of valves installed in a flow path of the first hydraulic pump P1 and shifted to control hydraulic fluid fed to working devices (right traveling motor, arm, and so forth); the second switching valve B composed of valves installed in a flow path of the second hydraulic pump P2 and shifted to control hydraulic fluid fed to working devices (left traveling motor, boom, and so forth); and the third switching valve C composed of valves installed in a flow path of the third hydraulic pump P3 and shifted to control hydraulic fluid fed to a swing device and so on. However, since these constituent elements are substantially the same as those of the circuit as illustrated in FIG. 1, the detailed description thereof will be omitted. The same drawing reference numerals are used for the same elements across various figures.
As illustrated in FIGS. 1 and 2, the conventional hydraulic circuits having an auto idle function requires a confluence circuit and separate auto idle signal lines, and this causes the construction of the signal lines to be complicated. In particular, the hydraulic circuit as illustrated in FIG. 2 has a very complicated signal lines.
In addition, since the signal line 7 passes through all the switching valves A, B, C, and D of the working devices and the traveling devices, the hydraulic fluid may leak through joint surfaces of the respective switching valves A, B, C, and D. Particularly, in a high-temperature working environment, the formed auto-idle pressure may become unstable due to the leakage of the hydraulic fluid.